1. Field of the Invention
The invention relates to a flat panel display device and a method of forming a passivation layer in the flat panel display device. More particularly, it relates to a method of forming a passivation layer deposited by means of an atomic layer deposition method through a surface chemical reaction between precursors, which include atomic elements of the passivation layer.
2. Description of the Prior Art
With an advent of 21st century of higher information era, researches and developments on a next-generation display device have increasingly been important. In particular, the development of materials for use in display devices for communications and computers is important and will be more important in the future. Among the flat panel displays, an organic electroluminescence (OEL) device or an organic light-emitting device (OLED) bears particular significance, because the display devices offer self-emitting lights.
The organic light-emitting device (OLED) has different characteristics from other flat panel display devices such as a liquid crystal display (LCD), a cathode ray tube (CRT), a plasma display panel (PDP), and the like. The OLED device is also recognized as a flat panel display device that can implement a foldable display technology, which can be a next-generation display device. The OLED device is currently available for a LCD back light or a portable display device.
In organic light-emitting device, electrons and holes form electron-hole pairs within a semiconductor material. The electron-hole pairs are recombined to emit light. Also, the organic light-emitting device emits the light of three primary colors under an operating voltage of below 10V, relatively low voltage level, and it can implement a high resolution and a natural color. Furthermore, the display device has advantages such as a low cost fabrication, flexibility, and a rapid response time.
The structure of the organic light-emitting device will be explained. The organic light-emitting device is an injection-type thin film device having a light-emitting layer and a transporting layer. The organic light-emitting device and an inorganic semiconductor device are common in that they are light-emitting devices using electron-hole pairs. However, unlikely the P-N junction LED in which recombination is governed by injection of the minority carriers at the junction interface, in the organic light-emitting device, all of the carriers that contribute light-emitting are injected from an external electrode. In other words, the carrier-injection type light-emitting device requires an efficient electron injection and electron transportation organic material. The stack structure of the organic light-emitting device is mainly classified into a single film and a multi-layer. In the present description, only the organic light-emitting device having the multi-layer structure will be described by reference to FIG. 1.
FIG. 1 is a cross-sectional view of the conventional organic light-emitting device of the multi-layer structure. The organic light-emitting device has a structure in which a substrate 10, an anode electrode 12, a hole injection layer 14, a hole transporting layer 16, an emitting layer 18, an electron transporting layer 20, an electron injection layer 22 and a cathode electrode 24 are stacked.
As described above, the organic light-emitting device has disadvantages that it is easily degraded by internal factors such as degradation of the cathode electrode due to oxygen, degradation of the light-emitting layer due to oxygen from ITO, degradation due to reaction between the light-emitting layer and the interface or the like, and by external factors such as moisture, oxygen, ultraviolet rays, manufacture conditions of the device, and the like. In particular, packaging of the organic light-emitting device is very important since external oxygen and moisture give a fatal effect on the lifetime of the device.
Only several technologies on packaging the organic light-emitting device have been reported. One of the technologies that have been widely used is a structure in which a passivation metal can 26 is covered over the cathode electrode as shown in FIG. 1.
Another technology of packaging the organic light-emitting device was disclosed in U.S. Pat. No. 5,952,778 (hereinafter called ‘778 patent’) entitled ‘Encapsulated Organic light-emitting device’ issued on Mar. 18, 1997. The 778 patent discloses a method which a metal relatively less sensitive to moisture or oxygen, for example Al or transition metals, etc. is deposited on the cathode electrode of the organic light-emitting device. By using same mask as the cathode electrode, an inorganic insulating film (for example, a silicon oxide film, a silicon nitride film, etc.) is formed under a vacuum. The deposition method may include an ion beam deposition method, an electron beam deposition method, a plasma beam deposition method, a chemical vapor deposition method, or the like. Hydrophobic polymers such as polysiloxane, polytetrafluethtylene, etc. are formed on the inorganic insulating film, thus the organic light-emitting device being encapsulated.
U.S. Pat. No. 5,496,597 relates to a thin inorganic insulating film manufactured by means of the atomic layer deposition method. This technology presents a new method using various organometallic compounds in order to form a dielectric layer of the electroluminescent display device. However, this conventional method discloses only a high temperature process, which is useful for the fabrication of dielectric thin film having high breakage strength and a low leakage current.
Furthermore, another prior art is an article entitled ‘Dependence of Atomic layer-Deposited Al2O3layers Characteristics on Growth Temperature and Al Precursor of Al(CH3)3and AlCl3 that was reported in J. Vac. Sci. Technol. A by S. J. Yun (1997). This article discloses a technology relating to variations in the characteristics depending on the type and growth temperature of an Al precursor in forming the Al2O3 insulating film. Like the '778 patent, this prior art discloses only a high temperature process of over 250° C.
As described above, the methods of fabricating the inorganic insulating film according to the prior arts have disadvantages that the deposition temperature is relatively high, the step coverage of the thin film is poor and the density thereof is not good. Therefore, a method capable of forming the inorganic insulating film at low temperature and having good characteristics is required.
As the information society is rapidly progressed, needs for a versatile and highly qualified display technology is increased. Plastic substrate for a foldable display device or a flexible display device is easily deformed under high temperature process. It is, therefore, inevitably necessary to manufacture an inorganic insulating film at a low temperature so that a cheap plastic is not deformed during the manufacturing the display such as a digital paper as well as the organic light-emitting device, on the plastic substrate.